have just noticed a bolt missing just above the modulator, in the black circle that is where the modulator thingy goes and in the red circle is a threaded hole not sure what its for? it doesnt leak trans fluid or anything and has clean thread

sorry about the angle of the picture, if you tilt your head to the right its the right way

Above the modulator is a cooler line. The modulator is held in by a spring metal clamp- that's what is under the bolt that holds the modulator in.